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Fair value of derivative asset subject to concentration of credit or market risk or both.

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Net gain (loss) relating to components of the gain (loss) on the fair value hedging instrument excluded from the assessment of fair value hedge effectiveness. Recognized in earnings.

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Derivative Financial Instruments - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Derivative
Aggregate fair value of all derivative instruments with credit risk-related contingent features in a liability position	$ 255.7	$ 116.2
Derivative, Notional Amount	3,751.4	2,983.7
Approximate amount of net deferred gains on derivative instruments expected to be amortized during the next twelve months	$ 9.2
Maximum Length of Time Hedged in Cash Flow Hedge	39 years
Component of Derivative Gain (Loss) Excluded from the Assessment of Hedge Effectiveness	$ (22.0)	(21.1)	$ 17.6
Discontinued Hedge Accounting Due to Instrument No Longer Qualifying as Fair Value Hedge	0.0	0.0	$ 0.0
Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	3,445.5	2,697.0
Not Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	305.9	286.7
Cash Flow Hedging \| Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	2,709.1	2,054.5
Interest Rate Swaps \| Not Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	125.9	132.0
Interest Rate Swaps \| Cash Flow Hedging \| Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	139.1	149.5
Interest Rate Swaps \| Fair Value Hedging \| Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	736.4	642.5
Forwards \| Not Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	51.1	52.5
Forwards \| Cash Flow Hedging \| Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	2,570.0	1,905.0
Total Return Swap \| Not Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	128.9	102.2
Receive Fixed/Pay Fixed \| Interest Rate Swaps \| Not Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	125.9	132.0
Receive Fixed/Pay Fixed \| Interest Rate Swaps \| Cash Flow Hedging \| Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	139.1	149.5
Receive Fixed/Pay Fixed \| Interest Rate Swaps \| Fair Value Hedging \| Designated as Hedging Instrument
Derivative
Derivative, Notional Amount	736.4	642.5
Credit Exposure
Derivative
Credit Exposure on Derivatives	$ 0.5	$ 1.6